1. Field of the Invention
The present invention relates to a backlight assembly and an LCD having the same.
2. Description of the Related Art
A current trend in the development of display devices is to replace the cathode ray tube (CRT) with a liquid crystal display (LCD) or a plasma display panel (PDP). The LCD has been found to have lower power consumption, slimmer profile, and lighter weight compared with the CRT. In addition, LCD devices do not generate harmful electromagnetic waves. For these reasons, LCD devices are considered the next generation in display device technology.
Generally, an LCD includes a lower substrate on which thin film transistors (TFTs) are formed, an upper substrate on which color filters are formed, and a liquid crystal layer formed between the lower substrate and the upper substrate. The TFTs transmit and control electric signals to generate voltages. These generated voltage in turn change the molecular structure of the liquid crystals injected in the liquid crystal layer thereby controlling the transmittance of light to display desired colors and images.
Since the LCD displays an image by controlling light incident from outside, it requires an additional light source, for example, a backlight assembly, to irradiate light onto the liquid crystal panel. Backlight assemblies are generally classified into an edge type or a direct type according to the position of the light source with respect to a display panel. Of the two types, the direct type backlight assembly is more widely used in a large-sized LCD devices because of its high optical utilization and lack of size limitations.
An external light source for a direct type backlight assembly is selected based on the size and purpose of use of the LCD. The external light source may include a point light source such as a light bulb or a white halogen lamp, a line light source such as a fluorescent lamp, and a surface light source such as a light emitting diode (LED) of an electro luminescent (EL) or matrix type.
Cold cathode fluorescent lamps (CCFL) that have generally been used as the light source are gradually being replaced with external electrode fluorescent lamps (EEFL) due to the fact that a plurality of EEFLs may be controlled by one inverter. The resulting decrease in parts causes a great reduction in manufacturing costs and weight of the LCD.
FIG. 1 is an exploded perspective view of a direct type backlight assembly according to the related art and FIG. 2 is an enlarged perspective view illustrating the connection between an EEFL and a side support of the backlight assembly of FIG. 1.
Referring to FIGS. 1 and 2, the direct type backlight assembly 1 includes a plurality of lamps 13 having external electrodes 15 formed on each end, side supports 17 for supporting the plurality of lamps 13, a diffusion plate 19, and a bottom plate 11 positioned above and below the plurality of lamps 13, respectively.
A driving voltage (not shown) is applied to the external electrodes 15 and the lamp 13 emits light. Accordingly, these lamps are referred to as EEFLs.
The external electrodes 15 are inserted inside the side supports 17. To prevent the external electrodes from being exposed outside of the side supports 17, the length of the external electrodes 15 must be less than or equal to the width of the side support. However, reducing the length of the external electrodes results in increased driving voltage for the lamp 13 Large-sized LCD panels require longer EFFLs resulting in even higher driving voltages. Consequently, it is difficult to apply the EEFL to the LCD.
One approach to reduce the driving voltage of the EEFL is to increase the length of the external electrodes thereby expanding the surface area of the external electrode and decreasing the required driving voltage. However, this approach requires that the width of the side supports or bezel be widened to cover the increased length of the external electrodes with increases the non-viewable area of the LCD device.
In order to prevent the bezel width from being widened and expand the length of the external electrodes, approaches have been developed which expose the external electrode out of the side support toward an inner space of the backlight assembly, as shown in FIG. 3B. However, backlight assemblies made in accordance with these approaches, degrade picture quality due to darkness because the exposed external electrode does not emit light well as discussed below with reference to FIGS. 3A and 3B.
As shown in FIG. 3A, when the entire surface of the external electrodes is inserted into the side support 17, only the lamp 13 is exposed out of the side support 17. Accordingly, images are displayed with uniform picture quality on a liquid crystal panel 31. However, as shown in FIG. 3B, when the external electrode 15 and the lamp 13 are exposed out of the side support 17, images are not displayed with uniform quality. More specifically, the picture quality is degraded in the area corresponding to the exposed external electrode. This degradation in picture quality is referred to as a mura 33. Since the external electrode 15 is not a light emission region, a dark region exists. Due to the mura 33, the picture quality is degraded.
Also, as shown in FIG. 3B, when the external electrode 15 is exposed out of the side support 17, an operator may be injured by high voltage when assembling the backlight assembly.